Particular embodiments generally relate to systems, circuits, and devices for communicating data signals over increased voltage direct current (DC) power line cables.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In an attempt to simplify the implementation and deployment of data transmission and networking infrastructures, various systems exist for sending data over power transmissions lines. Data transmission systems that use existing power transmission lines and wires for data communication are referred to as power line communication (PLC) systems. PLC systems have the distinct advantage of reducing the cost and complexity associated with deploying, installing, and maintaining separate data transmission wires or fiber optic cable required for other physical connection-based networking systems, such as Ethernet, digital subscriber lines (DSL) or high-speed internet cable or fiber optic systems. However, transmitting and receiving data and power on the same wires or cables presents a particular set of problems and drawbacks.
For example, receiving data over a power line, such as a conventional household electrical system of wires, breakers, switches and outlets, requires specialized transceivers that can both receive the composite power/data signals and separate or filter the data signal from the alternating current (AC) or the direct current (DC) electrical power delivered at a particular voltage. FIG. 1 shows a simplified schematic of a conventional system 100 for transmitting and receiving data over electrical power lines. As shown, the system 100 includes transmitter/receiver or transceiver 105 coupled to the supply unit 120 via the power wires 110. The power wires are typically the wires of a residential or commercial electrical system and include isolated positive and negative wires. The actual electrical power signal can be generated, transmitted and routed to transceiver 105 by another entity, such as a municipal or private electrical power company. In such systems, the electrical power can be provided in a variety of voltages, currents, and signal types and the transceiver 105 can be coupled to that existing electrical power supply system at a location local or remote to the supply unit 120. Typical household electrical power in North America is provided at approximately 50 Hz AC, 120V and 15 A, while in Europe and Asia, electrical power is provided at 50-60 HZ AC, 220-240V and 10-20 A.
Inside the supply unit 120, is a collection of components used for converting the received electrical power from one voltage to another, from one current to another, and/or from AC to DC, while also detecting any included data signals from the transceiver 105. As shown, supply unit 120 includes an AC/DC and DC/DC converter 121 coupled to power wires 110 to convert the received electrical power to the voltage, current, and type of power required by the network device 130 over DC supply line 113. The supply box 120 also includes a zero-crossing detection module 123 coupled to the power lines 110. The zero-crossing detection module 123 can sense the frequency of an AC power signal by determining the number of times the AC power signal goes from the positive to negative and negative to positive in a given time period. The zero-crossing can be counted or otherwise sensed in both the positive-to-negative direction and negative-to-positive direction, or in only one of the directions. In any scenario, the zero-crossing detector 123 can provide the zero-crossing events to the digital base-band unit 127 over connection 111 data for PLC timing purposes.
Also connected to the power lines 110 is the PLC analog front-end module 125. PLC analog front end module 125 can receive both the electrical power signal and the data signal over the electrical wires 110 from transceiver 105. PLC analog front end module 125 filters the data signal from the electrical power signal. PLC analog front end module 125 sends the data signal filtered from the composite electrical power and data signal to the digital base-band module 127. Digital baseband module 127 can then send a modulated digital data signal to a network device 130 over a network connection 115. Network connection 115 can be any type of data for network communication including, but not limited to USB, Ethernet, IEEE 1394, IEEE 1903, IEEE 1901, and other data and network cables, wires and connections.
As can be seen in FIG. 1, to deliver both electrical power signals and data signals from the supply unit 120 to the network device 130 requires two physical wire connections; DC supply connection 113 and network connection 115. To simplify the connection between the supply unit 120 and the network device 130, some conventional solutions have reduced the number of physical wire connections between the supply unit and the network device from two to one. FIG. 2 shows one conventional solution (for example Power-over-Ethernet) for a simplified connection between supply unit 122 and network device 131 that using a single composite power/data connection or cable 117. In such solutions, the converted electrical power signal from AC/DC+DC/DC converter 121 is sent via dc supply connection 113 to be combined with the data signal filtered from the incoming composite electrical power and data signal.
In the example shown, the PLC module 129 includes both the analog front-end and the digital base-band capabilities. The PLC module 129 performs the same functions as PLC front-end module 125 and digital base-band module 127 described in reference to FIG. 1, and then sends the data signal and the zero-crossing data from the zero-crossing detector 123 to the network device 131 that is configured to receive a composite electrical power and digital data signal via composite power/data cable 117. Since power/data cable 117 is usually an Power-over-Ethernet cable, the power supplied is limited to approximately 100 mA. Such limited electrical power is often insufficient especially for many network devices, such as network gateways, network access points, network routers, Internet-enabled or multi-media television set-top boxes, and personal computers, because such devices usually require electrical power with voltages on the order of 1V to 10y. 
Drawbacks of using either of the solutions described in reference to FIGS. 1 and 2, stem from the inclusion of the AC/DC or DC/DC power converter 121 and the PLC module functionality in the same physical box as shown in supply units 120 and 122. Inexpensive and mass-produced AC/DC or DC/DC power converter 121 are more often than not the point of failure in supply units such as supply units 120 or 122. The cost of replacing a supply unit can be high based on the fact that the entire supply unit, including the expensive PLC module components, need to be replaced each time the commoditized AC/DC or DC/DC power converter 121 fails. Furthermore, inexpensive AC/DC or DC/DC power converters are often not designed with data communication in mind, so such AC/DC or DC/DC power converters can also generate internal electrical noise that can interfere with the data signal sent to the network device 130 or 131.